A dried-fruit stall in the covered market has two boards hanging above it, and for a week the customers argued about which one was the better offer.
The first board says: three kilograms for 24,000 som. The second says: six kilograms for 48,000 som. People who buy a lot pointed at the second board; people buying a little pointed at the first, and both sides felt they had found something.
Neither had. Divide, and the first board works out at 8,000 som a kilogram. Divide the second, and it works out at 8,000 som a kilogram. They are not two prices at all — they are the same offer written twice, once at three kilograms and once at double that.
The trader put the second board up because customers buying for a wedding asked what six kilograms would cost, and he was tired of doing the sum. It was never meant to be a discount.
There is a small lesson hiding in the argument. If you are told two things and the second is only the first multiplied by two, you have been told no extra information. Anything the first board can settle, it settles alone; anything it cannot settle, the second board cannot settle either.
The stall now has one board. Under the price the trader has written, in smaller letters: any quantity, at this rate.